Stereotactic body radiation therapy

There are basically two forms of stereotactic body radiation therapy system (SBRT) available today: the CyberKnife® system developed by Accuray and the RapidArc® system developed by Varian Medical Systems. Don’t be fooled by the use of terms like “robotic radiosurgery” — these are both types of radiation therapy, but they are very different from traditional forms of radiation therapy because:

  • They involve the use of very highly focused beams of photons to provide high-dose radiation to the prostate and
  • Radiation therapy with these two systems allows treatment to take place over just 5 visits to the radiation oncology treatment center as opposed to the 40 visits over 8 weeks that have been customary with even the most sophisticated forms of proton beam radiation and intensity-modulated radiation.

So the first and most obvious patient benefit of SBRT compared to other types of radiation therapy for prostate cancer is less hassle. And that is a big deal.

Both techniques take advantage of specialized methods to allow for radiation to be focused onto the prostate despite any movement of the prostate within the patient between treatments or even during treatment itself.

However, the downside of SBRT in the treatment of prostate cancer is equally obvious. We have very few data so far that give us any idea whether outcomes using SBRT will be as good, over time, as the outcomes achieved using high-dose forms of things like intensity-modulated radiation therapy (IMRT), image-guided radiation therapy (IGRT), and proton beam radiation therapy (PBRT). Hopefully they will be, and hopefully they may be at least as effective but with fewer adverse effects, but that will take time to discover.

Currently, The “New” Prostate Cancer InfoLink is aware of only three significant, published series of data on the clinical use of SBRT, all of which are based on patients treated with the CyberKnife system:

  • In October 2009, Friedland et al. published data on 112 patients with early stage prostate cancer treated between February 2005 and December 2006. All patients had clinical stage T1c-T2cN0M0 disease, and 81/112 had a Gleason score of 3 + 3 = 6. At the time of diagnosis their mean PSA was 6.0. The patients all received a total dose of 35-36 Gy administered in 5 consecutive fractions. At a median follow-up of 24 months, the patients’ average PSA value was 0.78 ng/ml. Two patients had had a local relapse, and one patient developed distant metastases. Acute side effects were said to be mild and to have resolved shortly after treatment. There was just one case of a Grade 3 rectal complication (bleeding) and 82 percent of the patients who said they were sexually potent before treatment also said that they had maintained erectile function post-treatment.
  • In February 2010, Katz et al. published data on a series of > 300 patients, and The “New” Prostate Cancer InfoLink has provided a separate and detailed report on these patients, who had been followed for up to 42 months at the time of that report.

All that we can really say about these types of radiation therapy as treatments for prostate cancer at this time is that the early results look promising but it will be at least another 3-5 years before we have enough data to be able to say with any degree of justification that these forms of radiation provide results as good or better than their predecessors. If they are as effective and safe as older treatments, there is little doubt that the saving in treatment time is certainly worth a lot for any man who values that time.

Content on this page last reviewed and updated April 21, 2010.
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